We have all been there—trying to enjoy a summer camping trip while the interior of the rig feels like a literal oven. Even the best factory cooling systems can struggle when the mercury hits triple digits or when you are parked in direct sunlight without shade.
Adding a second rooftop air conditioner is the most effective way to reclaim your comfort and ensure your family actually enjoys the trip. This guide will show you exactly how to install a 2nd rv ac unit so you can stop sweating and start relaxing in a crisp, cool environment.
In the following sections, we will break down the electrical requirements, the physical mounting process, and the pro tips that ensure a leak-free installation. Whether you are upgrading a 50-amp rig or modifying a 30-amp setup, we have the technical insights you need to succeed.
Assessing Your RV Power Capacity and Roof Structure
Before you lift a single tool, you must determine if your RV can handle the additional electrical load of a second compressor. Most modern RVs are pre-wired for a second unit, usually in the bedroom area where a standard 14×14-inch vent already exists.
If your rig has a 50-amp service, you likely have enough headroom to run two air conditioners simultaneously without much trouble. However, if you have a 30-amp service, you will need a power management system or a separate dedicated power inlet to avoid tripping the main breaker.
Check your roof’s structural integrity as well; most RV roofs are designed to support the weight of an AC unit (roughly 70–100 lbs). If you are replacing a vent, the framing is usually already reinforced, but it is always worth a quick inspection for soft spots or water damage.
Understanding the 30-Amp vs. 50-Amp Dilemma
A 50-amp RV provides 12,000 total watts of power, which is plenty for two or even three cooling units. A 30-amp RV only provides 3,600 watts, and a single 15k BTU AC unit can pull 1,500–1,800 watts on its own.
If you are on a 30-amp system, consider installing a soft start kit on both units to reduce the initial “startup surge.” This allows the compressors to kick on without overloading the circuit, making a dual-unit setup much more feasible.
Essential Tools and Materials for the Job
Having the right gear on hand prevents mid-project runs to the hardware store and ensures a professional-grade finish. You will be working on the roof, so safety gear like a sturdy ladder and non-slip shoes are your first priorities.
For the installation itself, you will need basic hand tools and some specialized RV supplies. Make sure your torque wrench is calibrated, as over-tightening the mounting bolts is a common mistake that leads to roof leaks later on.
- Non-leveling Dicor Lap Sealant: For sealing any roof penetrations or old screw holes.
- 12/2 Romex Wire: If your RV isn’t pre-wired, you’ll need this for the 20-amp circuit.
- Wire Strippers and Crimpers: For making clean, secure electrical connections.
- Butyl Tape: To provide a secondary water barrier under any mounting flanges.
- Multi-meter: Crucial for verifying that your power is off before you start and correct once finished.
Selecting the Right AC Unit
Choose a unit that matches your existing ductwork if you plan on tying the two systems together. However, many DIYers prefer a non-ducted unit for the second installation because it simplifies the process and provides a “blast” of cold air directly into the bedroom or garage area.
how to install a 2nd rv ac unit: A Step-by-Step Electrical and Mounting Guide
The first physical step in learning how to install a 2nd rv ac unit is removing the existing roof vent. Use a putty knife to carefully scrape away the old sealant and back out the screws holding the vent flange to the roof.
Once the vent is removed, clean the roof surface thoroughly with denatured alcohol or a dedicated RV roof cleaner. A clean surface is the only way to ensure the new foam gasket creates a watertight seal against the rubber or TPO membrane.
If your RV is pre-wired, you will find a coiled-up Romex wire tucked into the ceiling cavity near the vent opening. If not, you must fish a new wire from the 120V distribution panel through the ceiling or along the roofline using protective conduit.
Positioning the Unit on the Roof
Lifting a 90-pound AC unit onto an RV roof is the most dangerous part of the job; never try to do this alone. Use a material lift or a scaffolding system, or have two people on ladders while a third person helps guide it from the roof.
Carefully set the unit over the 14×14-inch opening, ensuring the thick foam gasket is centered. Do not slide the unit once it is on the roof, as this can tear the gasket or damage the roof membrane.
Wiring the New Circuit and Control Box
Safety is paramount here: ensure your RV is completely disconnected from shore power and your inverter is turned off. Open your main breaker panel and install a new 20-amp circuit breaker specifically for the new AC unit.
Route your 12/2 Romex wire into the breaker box, connecting the black wire to the breaker and the white wire to the neutral bus bar. The bare copper ground wire must be secured to the ground bus bar to prevent electrical shorts.
Inside the RV, you will install the ceiling template and the control box. This metal framework sandwiches the roof between the upper AC unit and the interior ceiling, providing the structural squeeze needed to seal the gasket.
Connecting the Thermostat
If you are using a wall-mounted thermostat, you will need to run low-voltage thermostat wire from the AC unit to the wall location. Many “direct-drop” units have the controls built into the ceiling assembly, which eliminates the need for extra wall wiring.
Ensure all wire nuts are tight and wrapped in electrical tape to prevent them from vibrating loose during travel. Secure the wiring harness according to the manufacturer’s diagram, usually matching color-coded wires for the fan and compressor.
Securing the Unit and Ensuring a Watertight Seal
The mounting bolts are the only thing holding your AC unit to the roof during 70-mph highway winds. Most manufacturers require you to tighten these bolts until the foam gasket is compressed by about 50 percent.
Look for the compression tabs on the gasket; these small plastic indicators will tell you when you have reached the correct tension. Do not use power tools for this step, as it is very easy to strip the threads or crush the roof structure.
Once the bolts are tight, reinstall the interior shroud and filters. On the roof, apply a bead of Dicor lap sealant around any new screw heads or wire entries, but do not seal the AC unit itself, as the gasket needs to be able to “breathe” and drain condensation.
Managing Condensation Runoff
Remember that AC units produce a lot of water as they dehumidify the air. Ensure the drain holes in the base pan of the unit are clear of any packaging material or debris so the water flows off the roof and not into your ceiling.
Testing and Troubleshooting Your Installation
Before you button everything up, it is time for the “smoke test.” Plug the RV into a 50-amp pedestal and flip the new breaker to the “on” position. Set the thermostat to “Cool” and the fan to “Auto.”
The fan should kick on immediately, followed by the compressor a few seconds later. Use an infrared thermometer to check the delta-T (the temperature difference between the intake air and the output air); you want to see at least a 15–20 degree drop.
If the compressor hums but doesn’t start, or if you hear a clicking sound, double-check your voltage at the unit. Low voltage is the primary killer of RV air conditioners, so ensure your extension cords or shore power cables are appropriately rated.
Frequently Asked Questions About How to Install a 2nd RV AC Unit
Can I install a 2nd AC unit on a 30-amp RV?
Yes, but you cannot run both units and a microwave or water heater at the same time. You will likely need to install a SoftStartRV device on the units to prevent the initial power surge from tripping your main 30-amp breaker.
Do I need to reinforce my RV roof?
In most cases, if you are replacing a standard 14×14 vent, the roof is already framed to handle the weight. However, if you are cutting a new hole where one didn’t exist, you must build a wooden or aluminum frame between the roof rafters to support the unit.
How long does it take to install a second AC?
For a DIYer with basic electrical knowledge, the process usually takes 4 to 6 hours. This assumes the RV is pre-wired; if you have to run new Romex through the ceiling, expect the job to take a full weekend.
What is the best sealant for an RV AC installation?
The AC unit itself uses a closed-cell foam gasket and does not require liquid sealant. However, for any wire penetrations or mounting screws for the shroud, use Dicor 501LSW non-leveling lap sealant for the best long-term results.
Final Thoughts on Your Cooling Upgrade
Taking the time to learn how to install a 2nd rv ac unit is one of the best investments you can make in your mobile lifestyle. It transforms your rig from a summer sweatbox into a true sanctuary, allowing you to camp in desert climates or humid coastal regions with total confidence.
Always prioritize safety when working on the roof and dealing with high-voltage electricity. If you feel unsure about the wiring schematics or your roof’s load-bearing capacity, do not hesitate to consult a professional technician for a quick inspection before you finalize the job.
With your new dual-AC setup, you are ready to tackle the hottest trails and the sunniest campsites. Stay cool, keep your gear maintained, and enjoy the comfort of a job well done. Stay safe and stay comfortable!
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